Credit

Caption

Gravitational lens. Diagram showing the principles behind a gravitational lens. Light from a distant star (top left) is bent by the gravitational field of a free-floating planet (black, centre). As the planet passes between the star and the Earth, the focusing of the light causes an increase (peak at lower right) in the star's observed brightness. The duration of this increase reveals the mass of the planet. For small masses, the effect is called microlensing. Gravitational microlensing is a way to detect the non-luminous portion of dark matter. This also includes objects such as neutron stars and black holes (stellar remnants), or brown dwarf stars (small stars that failed to ignite).